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Antifungal jujubogenin saponins from Colubrina retusa
X C Li1, H N ElSohly, A C Nimrod
1National Center for the Development of Natural Products, Research Institute of Pharmaceutical Sciences and Department of Pharmacognosy, School of Pharmacy, The University of Mississippi, University, Mississippi 38677, USA.
Abstract:
Antifungal assay-guided isolation of the 95% ethanol extract of the stems of Colubrina retusa yielded jujubogenin 3-O-alpha-L-arabinofuranosyl(1-->2)-[beta-D-glucopyranosyl (1-->3)]-alpha-L-arabinopyranoside (1), which showed modest growth-inhibitory effects against Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus (MICs, 50 microg/mL). In addition, two new minor saponins, jujubogenin 3-O-alpha-L-arabinofuranosyl(1-->2)-[2-O-(trans, cis)p-coumaroyl-beta-D-glucopyranosyl(1-->3)]-alpha-L-arabinopy ranosi de (2), and jujubogenin 3-O-(5-O-malonyl)-alpha-L-arabinofuranosyl (1-->2)-[beta-D-glucopyranosyl(1-->3)]-alpha-L-arabinopyranoside (3), were obtained. Saponin 2 was marginally active against only C. neoformans, with a MIC of 50 microg/mL, while 3 was inactive. NMR spectroscopy was used extensively for the structure determination of these compounds. The previously reported ambiguity of the NMR assignments of jujubogenin saponins for carbons -26 to -29 was clarified by a comprehensive analysis of the NMR spectra of 1.